1. Field of the Invention
This invention relates to apparatus for sequentially presenting photographs at a projection position whereat their images may be transmitted onto a viewing screen.
2. Description of the Prior Art
Apparatus for sequentially presenting photographs including transparent slides at a projection station or position are well known and generally include a supply chamber for receiving and supporting a plurality of photographs in a stack and a mechanism for sequentially removing an endmost photograph from the stack and advancing it to a projection position whereat its image may be transmitted by a suitable light source onto a viewing screen.
One of the problems with apparatus of the type described is that the sliding movement between the endmost photograph and the next adjacent photograph in the stack, during movement of the endmost photograph into the projection position, may cause damage to one of the photographs. For example, such sliding movement may cause scratching of the image bearing surface of the photographs or, in the case where the photograph is a slide, such movement may be impeded by reason of interference between the edges of the aperture of the slide being moved and the edges of the aperture of the adjacent slide in the stack.
It has been suggested that the above problem may be obviated by positioning the endmost photograph and the next adjacent photograph at an acute angle relative to each other during movement of the endmost photograph into the projection position. Specifically, see U.S. Pat. No. 3,038,270 granted to H. A. Nagel on June 12, 1962 wherein a stack of photographs is supported at a slight angle to a wall of a guideway which leads to a projection position or station. This is accomplished in part by providing the wall with a pair of spaced projections which are adapted to engage the trailing end portion of the endmost photograph for tilting the entire stack at a slight angle relative to the wall of the guideway. The Nagel apparatus includes a changer which is moved in a direction so as to engage the endmost photograph by its trailing end and move its leading edge into a second guideway which is coplanar with the first mentioned guideway. In other words, initial movement of the changer forces the leading edge of the photograph into the second guideway while the trailing end of the photograph is still maintained at an angle with respect to the first guideway. In this position, the photograph is partially bent with the leading end portion thereof parallel with the first guideway and the trailing end portion thereof at an angle thereto. Upon further movement of the photograph, the trailing end portion is no longer maintained or held at an angle with respect to the first guideway and the inherent resiliency in the bent photography causes the trailing end portion thereof to be urged into contact with the first guideway. At this stage of changer movement, a cam formed thereon engages the photograph adjacent the one being moved and further advance of the changer, tilts the adjacent photograph and the remaining photographs in the stack away from the first guideway thereby increasing the angle between the remaining photograhs and the first guideway. Further downward movement of the changer moves a roller into engagement with the photograph adjacent to the one being moved thereby reducing the sliding friction between the cam and the adjacent photograph for minimizing the likelihood of any damage thereto.
While the above described patent recognizes the problem involved in sliding an endmost photograph off of a stack of photographs, it does not go far enough in the solution of the problem. To the contrary, it creates new problems, i.e., the bending of the leading end portion of the photograph as it is entering the second guideway and the friction created between the cam and the next adjacent photograph. Therefore, it can be readily appreciated that there still remains a need to provide an apparatus of the type described which will remove an endmost photograph from a stack of photographs and advance it to a projection position without bending it during such movement. Also the apparatus must keep the frictional engagement between the endmost photograph and the next adjacent photograph a minimum during such movement.